German Patent Application No. DE-OS 41 06 102 shows a pressure sensor including a pressure plunger, located in a sensor housing, that can be acted upon by the pressure being measured and guided in a linearly displaceable fashion such that one end of the pressure plunger rests orthogonally on a sensor membrane. The sensor membrane is part of a micromechanical arrangement made of silicon. The sensor membrane is deflected when acted upon by pressure, thus generating an analyzable measurement signal corresponding to the pressure introduced by the pressure plunger. A measurement signal is detected piezoresistively via a bridge circuit, and analyzed in an attached electronics unit.
In the above arrangement, it is necessary to apply the force of the pressure plunger onto the sensor membrane in as well-defined and homogeneous a manner as possible so as not to produce any measurement errors due to inaccurate conformity between the contact surface of the plunger end and the sensor membrane surface, or due to additional transverse stresses in the sensor membrane. This can result from tolerances and angular errors in the orthogonal alignment of the pressure plunger on the sensor membrane, or from irregularities in the contact surfaces.
The above-document contains several proposals to eliminate this problem. In a first embodiment, the entire pressure plunger is manufactured from soft material, so that its contact surface adapts conformingly to the sensor membrane. This conflicts, however, with the need for a pressure plunger of high rigidity. In a further embodiment, therefore, it is proposed that the plunger be produced, for the greater part of its length, from glass ceramic constituting a relatively hard material with low thermal conductivity, with only the end region being made from a relatively soft metal, for example aluminum, brass, copper, or plastic. To do so, however, it is necessary to extend the pressure plunger at its end with soft material, which is relatively complex and entails additional tolerance problems.
In a further embodiment, an intermediate element is arranged on the sensor membrane to convey the force of the pressure plunger into the sensor membrane homogeneously and with an accurately defined contact surface. This intermediate element is made of borosilicate glass or also of silicon, and has a high-quality surface finish. The intermediate element is bonded to the sensor membrane anodically or directly. With the intermediate element made of relatively hard material, homogeneous force application and a defined contact surface are achieved by accurate alignment and high surface quality, with relatively high manufacturing complexity.